Low profile glass enclosed hermetically sealed circuit breaker

ABSTRACT

A circuit breaker comprises a bimetal snap-action element disposed within a hermetically sealed glass envelope. The snapaction element opens an electrical circuit upon thermal or current overload. The glass envelope has two substantially flat parallel sides in order to provide a low profile to the circuit breaker and to improve thermal transfer to the snap-action element.

United States Patent [1 1 Dennis Aug. 14, 1973 {5 LOW PROFILE GLASSENCLOSED 3.227.842 1/1966 Salem 337/112 x HERMETICALLY SEALED cmcun3,278,705 10/1966 Dennis 337/362 BREAKER Inventor: Philip J. Dennis,Cape Elizabeth,

Maine Assignee: GTE Sylvnnla Incorporated,

Danvers, Mass.

Filed: Mar. 20, 1972 Appl. No.: 235,903

US. Cl. 337/112, 337/89, 337/365, 337/380 Int. Cl. "01h 45/02Fleldolsearch 337/112, 113, 89, 337/365, 380, 362

References Cited UNITED STATES PATENTS Dales 337/380 X PrimaryExaminer-Bernard A. Gilheany Assistant Examiner-F. E. Bell A norne vNorman OMalley and James Theodosopoulos [57] ABSTRACT A circuit breakercomprises a bimetal snap-action element disposed within a hermeticallysealed glass envelope. The snap-action element opens an electricalcircuit upon thermal or current overload. The glass envelope has twosubstantially flat parallel sides in order to provide a low profile tothe circuit breaker and to improve thermal transfer to the snap-actionelement.

3 Claims, 2 Drawing Figures I l N Patented Aug. 14, 1973 FIG. 1

. art glass enclosed circuit breakers.

1 LOW PROFILE GLASS ENCLOSED IIERMETICALLY SEALED CIRCUIT BREAKERBACKGROUND OF THE INVENTION 1. Field of the Invention This inventionpertains to glass enclosed hermetically sealed circuit breakerscontaining a bimetal snapaction element which is normally in a closedposition.

2. Description of the Prior Art Circuit breakers of the type with whichthis invention is concerned are shown in the following U. S. Pat. Nos.3,272,944; 3,278,705; 3,278,706; 3,307,126; 3,555,478; 3,573,696;3,573,697; and 3,597,838.

The breakers comprise two lead-in wires extending through a seal of ahermetically sealed glass envelope, a bimetal snap-action elementmounted on one of the lead-in wires and a contact mounted on the otherleadin wire. In normal operation the snap-action element is closed, thatis to say, is in electrical contact with the contact mounted on theother lead-in wire. The circuit breaker is attached to an electricaldevice being protected, such as a motor, fluorescent lamp ballast,electrical heater and the like, so that some or all of the electriccurrent passes. through the snap-action element. Thus, when a faultoccurs and the electrical device starts to draw excessive current, saidcurrent will overheat (1 R losses) the snap-action element and cause itto snap open, thereby opening the electrical circuit.

In addition, the circuit breaker is physically located in such proximityto the electrical device that if thermal overload of the device occurs,the snap-action element will eventually be heated above its snaptemperature and open the circuit. It can be seen, then, that it isadvantageous to mount the circuit breaker as close to the heated part ofthe electrical device as possible and with efficient heat transfertherebetwe'en, in order to obtain prompt circuit interruption uponabnormal temperature rise of the device.

In motors, for example, a desirable location for a circuit breaker isadjacent the stationary field coils. However, the cyindrical shape ofglass envelopes of the prior art circuit breakers often obviates such alocation where the motor housing is a close fit around the stationaryfield coils. And although prior art metal or plastic enclosed circuitbreakers have flat shapes to fit into tighter locations than glassenclosed circuit breakers, they do not have the advantages of thelatter, especially as relates to hermetic sealing, low cost and ease ofadjusting snap temperature just prior to final sealing.

It is an object of this invention to provide a glass enclosedhermetically sealed circuit breaker that has a lower profile and betterheat transfer than such prior SUMMARY OF THE INVENTION A circuit breakerin accordance with this invention comprises a hermetically sealed glassenvelope having a flat press seal at one end thereof. Extending throughThe glass envelope has two substantially flat parallel sides, roughlydescribable as a flattened ellipse, and is made by heating cylindricaltubing to the softening point and then pressing between parallel jaws toobtain the desired flattened shape. The snap-action element is mountedwithin the envelope so as to be substantially parallel to the flat sidesthereof.

BRIEF DESCRIPTION OF THE DRAWING FIG. I is an elevational view and FIG.2 a crosssectional view of a circuit breaker in accordance with thisinvention.

DESCRIPTION or THE PREFERRED EMBODIMENT As shown in the drawing, acircuit breaker has a glass envelope 1 having a flattened ellipticalshape. One end of envelope 1 is sealed by a press seal 2. Embeddedwithin press seal 2 and extending interiorly and exteriorly therefromare lead-in wires 3 and 4. Welded to the upper end of lead-in wire 4 isa substantially flat bir'netal snap-action element 5 having a contactbutton 6 welded thereto at the upper end thereof. A similar contactbutton 7 is welded to the upper end of lead-in wire 3. Normally, thecircuit breaker is in a closed position, that is to say, buttons 6 and 7are touching.

In order to provide a low profile to the circuit breaker, element 5,which is the widest component within envelope 1, is mountedsubstantially parallel to the flat sides of envelope 1.

In one aspect of the invention, the distance between element 5 and theflat glass wall therebehind is kept small,,say, about 30 to mils, sothat the glass limits the movement of element 5 when it snaps open. Thereason for this is to limit the gap distance between buttons 6 and 7 andthereby prevent excessive arcing, as discussed in U. S. Pat. No.3,555,478 which is incorporated herein by reference.

In the manufacture of the circuit breaker, a length of open-ended glasstubing was prepared, longer than the finished length of envelope 1. Forexample, for a circuit breaker having an overall envelope length of 1inches, the glass tubing had a length of 2 :6 inches. The outsidediameter of the tubing was 9/32 inch.

About 1 inch of the tubing was heated and pressed, as describedpreviously, so that the width of the glass between the flats was 13/64inch outside. This increased the elliptical diameter to 11/32 inchoutside.

The circuit breaker assembly, consisting of wires 3 and 4 with elements5, 6 and 7 mounted thereon,was inserted into the flattened glass tubingand supported externally by means of wires 3 and 4. An elongated toolwas inserted into the other end of the tubing to support.

snap element 5 and wire 4. The reason for this was to prevent any changein the position of wire 4 relative to wire 3 and in the predeterminedsnap temperature of element 5, which could result from the intense heatof the flames used to form press seal 2. Press seal 2 was then formed,using suitable pressing jaws, after the glass was heated to thesoftening temperature. The pressing was perpendicular to the planeformed by wires 3 and 4 in order to prevent reduction of the gap betweenwires 3 and 4. Also, the jaws were shaped to contain the glass somewhatin order that press seal 2 be within the perimeter of envelope 1.Envelope 1 was then hermetically sealed by conventionally sealing theopen end of the tubing, which had not been flattened,

leaving residual sealed tip 8. If desired, envelope 1 could be filledwith a suitable inert atomsphere, such as nitrogen, through the opentubular end prior to final sealing.

I claim:

1. A glass enclosed, hermetically sealed circuit breaker comprising: aglass envelope having a flattened elliptical shape, the flattened sidesthereof being substantially parallel to each other; a press seal at oneend of said envelope; two spaced apart lead-in wires embedded in saidpress seal extending interiorly and exteriorly therefrom; asubstantially flat bimetal snapaction element disposed within saidenvelope and mounted on the upper end of one of said lead-in wires, saidelement being substantially parallel to said flattened sides of saidenvelope; a first contact button centrally disposed on the upper end ofsaid element; a second contact button mounted on the upper end of theother of said lead-in wires, said buttons normally being in physical andelectrical contact with each other; and said element having apredetermined snapping temperature whereby, upon attainment of saidtemperature, said element snaps open and interrupts an electricalcircuit, the gap between said element and the proximate flattened sideof said envelope being small so that the envelope limits the travel ofsaid element upon opening thereof.

2. The circuit breaker of claim 1 wherein the distance between theflattened sides of said envelope is less than the distance between thecurved sides of said elliptical shape.

3. The circuit breaker of claim 2 wherein the gap between said elementand the proximate flattened side of said envelope is about 30 to mils.

l i l

1. A glass enclosed, hermetically sealed circuit breaker comprising: aglass envelope having a flattened elliptical shape, the flattened sidesthereof being sUbstantially parallel to each other; a press seal at oneend of said envelope; two spaced apart lead-in wires embedded in saidpress seal extending interiorly and exteriorly therefrom; asubstantially flat bimetal snapaction element disposed within saidenvelope and mounted on the upper end of one of said lead-in wires, saidelement being substantially parallel to said flattened sides of saidenvelope; a first contact button centrally disposed on the upper end ofsaid element; a second contact button mounted on the upper end of theother of said lead-in wires, said buttons normally being in physical andelectrical contact with each other; and said element having apredetermined snapping temperature whereby, upon attainment of saidtemperature, said element snaps open and interrupts an electricalcircuit, the gap between said element and the proximate flattened sideof said envelope being small so that the envelope limits the travel ofsaid element upon opening thereof.
 2. The circuit breaker of claim 1wherein the distance between the flattened sides of said envelope isless than the distance between the curved sides of said ellipticalshape.
 3. The circuit breaker of claim 2 wherein the gap between saidelement and the proximate flattened side of said envelope is about 30 to60 mils.